For those watching TV, mesmerised after the first jet hit the World Trade Centre on 9/11, an awful certainty took over from a niggling fear as the second plane roared into its target.
This was no accident. Something terrible, contrived by man, had just happened. Within seconds it was clear that terrorism was involved. There were parallels on Tuesday night as word came in to Domodevo airport in Moscow of two planes downed almost simultaneously with a loss of 89 lives.
Investigators have been careful - in the absence of hard evidence - to allow for the possibility that human error or mechanical mishap contributed to a tragic coincidence of two accidents. But the disclosure that the pilots of one of the planes had triggered a hijack alert just before it crashed heightened suspicions that terrorists were involved. And in that context, attention focused on Chechen separatists whose predominant leader, Aslan Maskhadov, vowed in June to escalate attacks against Russians. "We're planning a change in our tactics," he said at the time. "From now on, we'll be launching big attacks." And, last month, in an e-mail to Reuters, he warned ominously that "if Chechens possessed warplanes or rockets, then airstrikes on Russian cities would also be legitimate".
His spokesman denied responsibilty in London yesterday but if terrorist involvement is confirmed and if Mashkadov's group was not responsible, the guilty are likely to be kindred souls. On Tuesday a Chechen attack injured four on a Moscow bus, and 23 Russian soldiers have been killed in Chechnya this week. In the past two years up to 500 have died in terrorist attacks on the Russian capital and in the battered southern province which is now entering its sixth year of war.
An escalation in violence appeared inevitable in the run-up to the election on Sunday to choose a successor to Akhmad Kadyrov, the Moscow-backed president of the republic who was assassinated in May. Separatists, who are boycotting an election from which their participation has in any case been banned, are determined to make polling as difficult as possible. Human rights organisations have already cast major doubts on the process.
Yet the truth is that neither side in this bloody war is capable of delivering a decisive strike against the other, or of pointing to a way out of the impasse. President Putin is bogged down, increasingly relying on a dwindling group of Chechens willing to identify with Russian rule and the brute force of an incompetent, indiscriminate army whose morale is at rock-bottom. The opposition, on the other hand, is incapable of inflicting more than pinprick military victories and has to resort instead to the "propaganda of the deed" in the form of terrorism to advertise its continuing struggle.
If terrorists are shown to have caused Tuesday's events, the tragedy will be compounded by the fact that it appears neither side is even close to taking the first small political steps needed to end the spiral of violence.